Add opacity control to MouseRegion. Add findAnnotations to Layer. (#37896)

* Adds a new parameter bool opaque to MouseRegion
* The same to RenderMouseRegion and AnnotatedRegionLayer
* Add findAnnotations to Layer 

packages/flutter/lib/src/gestures/hit_test.dart

@@ -54,7 +54,7 @@ class HitTestEntry {
   final HitTestTarget target;
 
   @override
-  String toString() => '$target';
+  String toString() => '${describeIdentity(this)}($target)';
 
   /// Returns a matrix describing how [PointerEvent]s delivered to this
   /// [HitTestEntry] should be transformed from the global coordinate space of

packages/flutter/lib/src/material/text_field.dart

@@ -878,9 +878,6 @@ class _TextFieldState extends State<TextField> implements TextSelectionGestureDe
     }
   }
 
-  void _handleMouseEnter(PointerEnterEvent event) => _handleHover(true);
-  void _handleMouseExit(PointerExitEvent event) => _handleHover(false);
-
   void _handleHover(bool hovering) {
     if (hovering != _isHovering) {
       setState(() {
@@ -1007,8 +1004,8 @@ class _TextFieldState extends State<TextField> implements TextSelectionGestureDe
     return IgnorePointer(
       ignoring: !_isEnabled,
       child: MouseRegion(
-        onEnter: _handleMouseEnter,
-        onExit: _handleMouseExit,
+        onEnter: (PointerEnterEvent event) => _handleHover(true),
+        onExit: (PointerExitEvent event) => _handleHover(false),
         child: AnimatedBuilder(
           animation: controller, // changes the _currentLength
           builder: (BuildContext context, Widget child) {

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -2591,8 +2591,9 @@ class RenderPointerListener extends RenderProxyBoxWithHitTestBehavior {
 
 /// Calls callbacks in response to pointer events that are exclusive to mice.
 ///
-/// Simply put, it responds to events that are related to hovering,
-/// i.e. when the mouse enters, exits or hovers a region without pressing.
+/// It responds to events that are related to hovering, i.e. when the mouse
+/// enters, exits (with or without pressing buttons), or moves over a region
+/// without pressing buttons.
 ///
 /// It does not respond to common events that construct gestures, such as when
 /// the pointer is pressed, moved, then released or canceled. For these events,
@@ -2601,14 +2602,21 @@ class RenderPointerListener extends RenderProxyBoxWithHitTestBehavior {
 /// If it has a child, it defers to the child for sizing behavior.
 ///
 /// If it does not have a child, it grows to fit the parent-provided constraints.
+///
+/// See also:
+///
+///  * [MouseRegion], a widget that listens to hover events using
+///    [RenderMouseRegion].
 class RenderMouseRegion extends RenderProxyBox {
   /// Creates a render object that forwards pointer events to callbacks.
   RenderMouseRegion({
     PointerEnterEventListener onEnter,
     PointerHoverEventListener onHover,
     PointerExitEventListener onExit,
+    this.opaque = true,
     RenderBox child,
-  }) : _onEnter = onEnter,
+  }) : assert(opaque != null),
+       _onEnter = onEnter,
        _onHover = onHover,
        _onExit = onExit,
        _annotationIsActive = false,
@@ -2620,10 +2628,24 @@ class RenderMouseRegion extends RenderProxyBox {
     );
   }
 
-  /// Called when a hovering pointer enters the region for this widget.
+  /// Whether this object should prevent [RenderMouseRegion]s visually behind it
+  /// from detecting the pointer, thus affecting how their [onHover], [onEnter],
+  /// and [onExit] behave.
+  ///
+  /// If [opaque] is true, this object will absorb the mouse pointer and
+  /// prevent this object's siblings (or any other objects that are not
+  /// ancestors or descendants of this object) from detecting the mouse
+  /// pointer even when the pointer is within their areas.
   ///
-  /// If this is a mouse pointer, this will fire when the mouse pointer enters
-  /// the region defined by this widget.
+  /// If [opaque] is false, this object will not affect how [RenderMouseRegion]s
+  /// behind it behave, which will detect the mouse pointer as long as the
+  /// pointer is within their areas.
+  ///
+  /// This defaults to true.
+  bool opaque;
+
+  /// Called when a mouse pointer enters the region (with or without buttons
+  /// pressed).
   PointerEnterEventListener get onEnter => _onEnter;
   set onEnter(PointerEnterEventListener value) {
     if (_onEnter != value) {
@@ -2637,10 +2659,8 @@ class RenderMouseRegion extends RenderProxyBox {
       _onEnter(event);
   }
 
-  /// Called when a pointer that has not triggered an [onPointerDown] changes
-  /// position.
-  ///
-  /// Typically only triggered for mouse pointers.
+  /// Called when a pointer changes position without buttons pressed and the end
+  /// position is within the region.
   PointerHoverEventListener get onHover => _onHover;
   set onHover(PointerHoverEventListener value) {
     if (_onHover != value) {
@@ -2654,10 +2674,7 @@ class RenderMouseRegion extends RenderProxyBox {
       _onHover(event);
   }
 
-  /// Called when a hovering pointer leaves the region for this widget.
-  ///
-  /// If this is a mouse pointer, this will fire when the mouse pointer leaves
-  /// the region defined by this widget.
+  /// Called when a pointer leaves the region (with or without buttons pressed).
   PointerExitEventListener get onExit => _onExit;
   set onExit(PointerExitEventListener value) {
     if (_onExit != value) {
@@ -2754,6 +2771,7 @@ class RenderMouseRegion extends RenderProxyBox {
         _hoverAnnotation,
         size: size,
         offset: offset,
+        opaque: opaque,
       );
       context.pushLayer(layer, super.paint, offset);
     } else {
@@ -2778,6 +2796,7 @@ class RenderMouseRegion extends RenderProxyBox {
       },
       ifEmpty: '<none>',
     ));
+    properties.add(DiagnosticsProperty<bool>('opaque', opaque, defaultValue: true));
   }
 }
 

packages/flutter/lib/src/rendering/view.dart

@@ -196,7 +196,9 @@ class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox>
     // Layer hit testing is done using device pixels, so we have to convert
     // the logical coordinates of the event location back to device pixels
     // here.
-    return layer.findAll<MouseTrackerAnnotation>(position * configuration.devicePixelRatio);
+    return layer.findAll<MouseTrackerAnnotation>(
+      position * configuration.devicePixelRatio
+    ).annotations;
   }
 
   @override
@@ -241,12 +243,12 @@ class RenderView extends RenderObject with RenderObjectWithChildMixin<RenderBox>
     final Rect bounds = paintBounds;
     final Offset top = Offset(bounds.center.dx, _window.padding.top / _window.devicePixelRatio);
     final Offset bottom = Offset(bounds.center.dx, bounds.center.dy - _window.padding.bottom / _window.devicePixelRatio);
-    final SystemUiOverlayStyle upperOverlayStyle = layer.find<SystemUiOverlayStyle>(top);
+    final SystemUiOverlayStyle upperOverlayStyle = layer.find<SystemUiOverlayStyle>(top)?.annotation;
     // Only android has a customizable system navigation bar.
     SystemUiOverlayStyle lowerOverlayStyle;
     switch (defaultTargetPlatform) {
       case TargetPlatform.android:
-        lowerOverlayStyle = layer.find<SystemUiOverlayStyle>(bottom);
+        lowerOverlayStyle = layer.find<SystemUiOverlayStyle>(bottom)?.annotation;
         break;
       case TargetPlatform.iOS:
       case TargetPlatform.fuchsia:

packages/flutter/lib/src/widgets/basic.dart

@@ -5575,11 +5575,11 @@ class Listener extends StatelessWidget {
     // TODO(tongmu): After it goes stable, remove these 3 parameters from Listener
     // and Listener should no longer need an intermediate class _PointerListener.
     // https://github.com/flutter/flutter/issues/36085
-    @Deprecated('Use MouseRegion.onEnter instead')
+    @Deprecated('Use MouseRegion.onEnter instead. See MouseRegion.opaque for behavioral difference.')
     this.onPointerEnter, // ignore: deprecated_member_use_from_same_package
-    @Deprecated('Use MouseRegion.onExit instead')
+    @Deprecated('Use MouseRegion.onExit instead. See MouseRegion.opaque for behavioral difference.')
     this.onPointerExit, // ignore: deprecated_member_use_from_same_package
-    @Deprecated('Use MouseRegion.onHover instead')
+    @Deprecated('Use MouseRegion.onHover instead. See MouseRegion.opaque for behavioral difference.')
     this.onPointerHover, // ignore: deprecated_member_use_from_same_package
     this.onPointerUp,
     this.onPointerCancel,
@@ -5656,6 +5656,7 @@ class Listener extends StatelessWidget {
         onEnter: onPointerEnter,
         onExit: onPointerExit,
         onHover: onPointerHover,
+        opaque: false,
         child: result,
       );
     }
@@ -5815,8 +5816,10 @@ class MouseRegion extends SingleChildRenderObjectWidget {
     this.onEnter,
     this.onExit,
     this.onHover,
+    this.opaque = true,
     Widget child,
-  }) : super(key: key, child: child);
+  }) : assert(opaque != null),
+       super(key: key, child: child);
 
   /// Called when a mouse pointer (with or without buttons pressed) enters the
   /// region defined by this widget, or when the widget appears under the
@@ -5832,6 +5835,22 @@ class MouseRegion extends SingleChildRenderObjectWidget {
   /// the pointer.
   final PointerExitEventListener onExit;
 
+  /// Whether this widget should prevent other [MouseRegion]s visually behind it
+  /// from detecting the pointer, thus affecting how their [onHover], [onEnter],
+  /// and [onExit] behave.
+  ///
+  /// If [opaque] is true, this widget will absorb the mouse pointer and
+  /// prevent this widget's siblings (or any other widgets that are not
+  /// ancestors or descendants of this widget) from detecting the mouse
+  /// pointer even when the pointer is within their areas.
+  ///
+  /// If [opaque] is false, this object will not affect how [MouseRegion]s
+  /// behind it behave, which will detect the mouse pointer as long as the
+  /// pointer is within their areas.
+  ///
+  /// This defaults to true.
+  final bool opaque;
+
   @override
   _MouseRegionElement createElement() => _MouseRegionElement(this);
 
@@ -5841,6 +5860,7 @@ class MouseRegion extends SingleChildRenderObjectWidget {
       onEnter: onEnter,
       onHover: onHover,
       onExit: onExit,
+      opaque: opaque,
     );
   }
 
@@ -5849,7 +5869,8 @@ class MouseRegion extends SingleChildRenderObjectWidget {
     renderObject
       ..onEnter = onEnter
       ..onHover = onHover
-      ..onExit = onExit;
+      ..onExit = onExit
+      ..opaque = opaque;
   }
 
   @override
@@ -5863,6 +5884,7 @@ class MouseRegion extends SingleChildRenderObjectWidget {
     if (onHover != null)
       listeners.add('hover');
     properties.add(IterableProperty<String>('listeners', listeners, ifEmpty: '<none>'));
+    properties.add(DiagnosticsProperty<bool>('opaque', opaque, defaultValue: true));
   }
 }
 

packages/flutter/lib/src/widgets/widget_inspector.dart

@@ -57,10 +57,14 @@ class _ProxyLayer extends Layer {
   }
 
   @override
-  S find<S>(Offset regionOffset) => _layer.find(regionOffset);
-
-  @override
-  Iterable<S> findAll<S>(Offset regionOffset) => <S>[];
+  @protected
+  bool findAnnotations<S>(
+    AnnotationResult<S> result,
+    Offset localPosition, {
+    @required bool onlyFirst,
+  }) {
+    return _layer.findAnnotations(result, localPosition, onlyFirst: onlyFirst);
+  }
 }
 
 /// A [Canvas] that multicasts all method calls to a main canvas and a
@@ -2662,10 +2666,14 @@ class _InspectorOverlayLayer extends Layer {
   }
 
   @override
-  S find<S>(Offset regionOffset) => null;
-
-  @override
-  Iterable<S> findAll<S>(Offset regionOffset) => <S>[];
+  @protected
+  bool findAnnotations<S>(
+    AnnotationResult<S> result,
+    Offset localPosition, {
+    bool onlyFirst,
+  }) {
+    return false;
+  }
 }
 
 const double _kScreenEdgeMargin = 10.0;

packages/flutter/test/rendering/annotated_region_test.dart

@@ -22,9 +22,9 @@ void main() {
         i += 1;
       }
 
-      expect(containerLayer.find<int>(const Offset(0.0, 1.0)), 0);
-      expect(containerLayer.find<int>(const Offset(0.0, 101.0)), 1);
-      expect(containerLayer.find<int>(const Offset(0.0, 201.0)), 2);
+      expect(containerLayer.find<int>(const Offset(0.0, 1.0)).annotation, 0);
+      expect(containerLayer.find<int>(const Offset(0.0, 101.0)).annotation, 1);
+      expect(containerLayer.find<int>(const Offset(0.0, 201.0)).annotation, 2);
     });
 
     test('finds a value within the clip in a ClipRectLayer', () {
@@ -41,9 +41,9 @@ void main() {
         i += 1;
       }
 
-      expect(containerLayer.find<int>(const Offset(0.0, 1.0)), 0);
-      expect(containerLayer.find<int>(const Offset(0.0, 101.0)), 1);
-      expect(containerLayer.find<int>(const Offset(0.0, 201.0)), 2);
+      expect(containerLayer.find<int>(const Offset(0.0, 1.0)).annotation, 0);
+      expect(containerLayer.find<int>(const Offset(0.0, 101.0)).annotation, 1);
+      expect(containerLayer.find<int>(const Offset(0.0, 201.0)).annotation, 2);
     });
 
 
@@ -61,9 +61,9 @@ void main() {
         i += 1;
       }
 
-      expect(containerLayer.find<int>(const Offset(5.0, 5.0)), 0);
-      expect(containerLayer.find<int>(const Offset(5.0, 105.0)), 1);
-      expect(containerLayer.find<int>(const Offset(5.0, 205.0)), 2);
+      expect(containerLayer.find<int>(const Offset(5.0, 5.0)).annotation, 0);
+      expect(containerLayer.find<int>(const Offset(5.0, 105.0)).annotation, 1);
+      expect(containerLayer.find<int>(const Offset(5.0, 205.0)).annotation, 2);
     });
 
     test('finds a value under a TransformLayer', () {
@@ -87,11 +87,11 @@ void main() {
         i += 1;
       }
 
-      expect(transformLayer.find<int>(const Offset(0.0, 100.0)), 0);
-      expect(transformLayer.find<int>(const Offset(0.0, 200.0)), 0);
-      expect(transformLayer.find<int>(const Offset(0.0, 270.0)), 1);
-      expect(transformLayer.find<int>(const Offset(0.0, 400.0)), 1);
-      expect(transformLayer.find<int>(const Offset(0.0, 530.0)), 2);
+      expect(transformLayer.find<int>(const Offset(0.0, 100.0)).annotation, 0);
+      expect(transformLayer.find<int>(const Offset(0.0, 200.0)).annotation, 0);
+      expect(transformLayer.find<int>(const Offset(0.0, 270.0)).annotation, 1);
+      expect(transformLayer.find<int>(const Offset(0.0, 400.0)).annotation, 1);
+      expect(transformLayer.find<int>(const Offset(0.0, 530.0)).annotation, 2);
     });
 
     test('looks for child AnnotatedRegions before parents', () {
@@ -101,7 +101,7 @@ void main() {
       parent.append(child);
       layer.append(parent);
 
-      expect(parent.find<int>(Offset.zero), 2);
+      expect(parent.find<int>(Offset.zero).annotation, 2);
     });
 
     test('looks for correct type', () {
@@ -111,7 +111,7 @@ void main() {
       layer.append(child2);
       layer.append(child1);
 
-      expect(layer.find<String>(Offset.zero), 'hello');
+      expect(layer.find<String>(Offset.zero).annotation, 'hello');
     });
 
     test('does not clip Layer.find on an AnnotatedRegion with an unrelated type', () {
@@ -121,7 +121,7 @@ void main() {
       parent.append(child);
       layer.append(parent);
 
-      expect(layer.find<int>(const Offset(100.0, 100.0)), 1);
+      expect(layer.find<int>(const Offset(100.0, 100.0)).annotation, 1);
     });
 
     test('handles non-invertable transforms', () {
@@ -133,7 +133,7 @@ void main() {
 
       parent.transform = Matrix4.diagonal3Values(1.0, 1.0, 1.0);
 
-      expect(parent.find<int>(const Offset(0.0, 0.0)), 1);
+      expect(parent.find<int>(const Offset(0.0, 0.0)).annotation, 1);
     });
   });
   group('$AnnotatedRegion findAll', () {
@@ -151,9 +151,9 @@ void main() {
         i += 1;
       }
 
-      expect(containerLayer.findAll<int>(const Offset(0.0, 1.0)), equals(<int>[0]));
-      expect(containerLayer.findAll<int>(const Offset(0.0, 101.0)),equals(<int>[1]));
-      expect(containerLayer.findAll<int>(const Offset(0.0, 201.0)), equals(<int>[2]));
+      expect(containerLayer.findAll<int>(const Offset(0.0, 1.0)).annotations.toList(), equals(<int>[0]));
+      expect(containerLayer.findAll<int>(const Offset(0.0, 101.0)).annotations.toList(), equals(<int>[1]));
+      expect(containerLayer.findAll<int>(const Offset(0.0, 201.0)).annotations.toList(), equals(<int>[2]));
     });
 
     test('finds a value within the clip in a ClipRectLayer', () {
@@ -170,9 +170,9 @@ void main() {
         i += 1;
       }
 
-      expect(containerLayer.findAll<int>(const Offset(0.0, 1.0)), equals(<int>[0]));
-      expect(containerLayer.findAll<int>(const Offset(0.0, 101.0)), equals(<int>[1]));
-      expect(containerLayer.findAll<int>(const Offset(0.0, 201.0)), equals(<int>[2]));
+      expect(containerLayer.findAll<int>(const Offset(0.0, 1.0)).annotations.toList(), equals(<int>[0]));
+      expect(containerLayer.findAll<int>(const Offset(0.0, 101.0)).annotations.toList(), equals(<int>[1]));
+      expect(containerLayer.findAll<int>(const Offset(0.0, 201.0)).annotations.toList(), equals(<int>[2]));
     });
 
 
@@ -190,9 +190,9 @@ void main() {
         i += 1;
       }
 
-      expect(containerLayer.findAll<int>(const Offset(5.0, 5.0)), equals(<int>[0]));
-      expect(containerLayer.findAll<int>(const Offset(5.0, 105.0)), equals(<int>[1]));
-      expect(containerLayer.findAll<int>(const Offset(5.0, 205.0)), equals(<int>[2]));
+      expect(containerLayer.findAll<int>(const Offset(5.0, 5.0)).annotations.toList(), equals(<int>[0]));
+      expect(containerLayer.findAll<int>(const Offset(5.0, 105.0)).annotations.toList(), equals(<int>[1]));
+      expect(containerLayer.findAll<int>(const Offset(5.0, 205.0)).annotations.toList(), equals(<int>[2]));
     });
 
     test('finds a value under a TransformLayer', () {
@@ -216,11 +216,11 @@ void main() {
         i += 1;
       }
 
-      expect(transformLayer.findAll<int>(const Offset(0.0, 100.0)), equals(<int>[0]));
-      expect(transformLayer.findAll<int>(const Offset(0.0, 200.0)), equals(<int>[0]));
-      expect(transformLayer.findAll<int>(const Offset(0.0, 270.0)), equals(<int>[1]));
-      expect(transformLayer.findAll<int>(const Offset(0.0, 400.0)), equals(<int>[1]));
-      expect(transformLayer.findAll<int>(const Offset(0.0, 530.0)), equals(<int>[2]));
+      expect(transformLayer.findAll<int>(const Offset(0.0, 100.0)).annotations.toList(), equals(<int>[0]));
+      expect(transformLayer.findAll<int>(const Offset(0.0, 200.0)).annotations.toList(), equals(<int>[0]));
+      expect(transformLayer.findAll<int>(const Offset(0.0, 270.0)).annotations.toList(), equals(<int>[1]));
+      expect(transformLayer.findAll<int>(const Offset(0.0, 400.0)).annotations.toList(), equals(<int>[1]));
+      expect(transformLayer.findAll<int>(const Offset(0.0, 530.0)).annotations.toList(), equals(<int>[2]));
     });
 
     test('finds multiple nested, overlapping regions', () {
@@ -237,7 +237,7 @@ void main() {
         parent.append(layer);
       }
 
-      expect(parent.findAll<int>(const Offset(0.0, 0.0)), equals(<int>[3, 1, 2, 0,]));
+      expect(parent.findAll<int>(const Offset(0.0, 0.0)).annotations.toList(), equals(<int>[3, 1, 2, 0,]));
     });
 
     test('looks for child AnnotatedRegions before parents', () {
@@ -251,7 +251,7 @@ void main() {
       parent.append(child3);
       layer.append(parent);
 
-      expect(parent.findAll<int>(Offset.zero), equals(<int>[4, 3, 2, 1]));
+      expect(parent.findAll<int>(Offset.zero).annotations.toList(), equals(<int>[4, 3, 2, 1]));
     });
 
     test('looks for correct type', () {
@@ -261,7 +261,7 @@ void main() {
       layer.append(child2);
       layer.append(child1);
 
-      expect(layer.findAll<String>(Offset.zero), equals(<String>['hello']));
+      expect(layer.findAll<String>(Offset.zero).annotations.toList(), equals(<String>['hello']));
     });
 
     test('does not clip Layer.find on an AnnotatedRegion with an unrelated type', () {
@@ -271,7 +271,7 @@ void main() {
       parent.append(child);
       layer.append(parent);
 
-      expect(layer.findAll<int>(const Offset(100.0, 100.0)), equals(<int>[1]));
+      expect(layer.findAll<int>(const Offset(100.0, 100.0)).annotations.toList(), equals(<int>[1]));
     });
 
     test('handles non-invertable transforms', () {
@@ -279,11 +279,11 @@ void main() {
       final TransformLayer parent = TransformLayer(transform: Matrix4.diagonal3Values(0.0, 1.0, 1.0));
       parent.append(child);
 
-      expect(parent.findAll<int>(const Offset(0.0, 0.0)), equals(<int>[]));
+      expect(parent.findAll<int>(const Offset(0.0, 0.0)).annotations.toList(), equals(<int>[]));
 
       parent.transform = Matrix4.diagonal3Values(1.0, 1.0, 1.0);
 
-      expect(parent.findAll<int>(const Offset(0.0, 0.0)), equals(<int>[1]));
+      expect(parent.findAll<int>(const Offset(0.0, 0.0)).annotations.toList(), equals(<int>[1]));
     });
   });
 }

packages/flutter/test/widgets/annotated_region_test.dart

@@ -34,12 +34,12 @@ void main() {
     int result = RendererBinding.instance.renderView.debugLayer.find<int>(Offset(
       10.0 * window.devicePixelRatio,
       10.0 * window.devicePixelRatio,
-    ));
+    ))?.annotation;
     expect(result, null);
     result = RendererBinding.instance.renderView.debugLayer.find<int>(Offset(
       50.0 * window.devicePixelRatio,
       50.0 * window.devicePixelRatio,
-    ));
+    )).annotation;
     expect(result, 1);
   });
 }

packages/flutter/test/widgets/mouse_region_test.dart

@@ -752,6 +752,196 @@ void main() {
     expect(paintCount, 1);
   });
 
+  group('MouseRegion respects opacity:', () {
+
+    // A widget that contains 3 MouseRegions:
+    //                           y
+    //   ——————————————————————  0
+    //   | ———————————     A  |  20
+    //   | | B       |        |
+    //   | |     ———————————  |  50
+    //   | |     |       C |  |
+    //   | ——————|         |  |  100
+    //   |       |         |  |
+    //   |       ———————————  |  130
+    //   ——————————————————————  150
+    // x 0 20   50  100   130 150
+    Widget tripleRegions({bool opaqueC, void Function(String) addLog}) {
+      // Same as MouseRegion, but when opaque is null, use the default value.
+      Widget mouseRegionWithOptionalOpaque({
+        void Function(PointerEnterEvent e) onEnter,
+        void Function(PointerExitEvent e) onExit,
+        Widget child,
+        bool opaque,
+      }) {
+        if (opaque == null) {
+          return MouseRegion(onEnter: onEnter, onExit: onExit, child: child);
+        }
+        return MouseRegion(onEnter: onEnter, onExit: onExit, child: child, opaque: opaque);
+      }
+
+      return Directionality(
+        textDirection: TextDirection.ltr,
+        child: Align(
+          alignment: Alignment.topLeft,
+          child: MouseRegion(
+            onEnter: (PointerEnterEvent e) { addLog('enterA'); },
+            onExit: (PointerExitEvent e) { addLog('exitA'); },
+            child: SizedBox(
+              width: 150,
+              height: 150,
+              child: Stack(
+                children: <Widget>[
+                  Positioned(
+                    left: 20,
+                    top: 20,
+                    width: 80,
+                    height: 80,
+                    child: MouseRegion(
+                      onEnter: (PointerEnterEvent e) { addLog('enterB'); },
+                      onExit: (PointerExitEvent e) { addLog('exitB'); },
+                    ),
+                  ),
+                  Positioned(
+                    left: 50,
+                    top: 50,
+                    width: 80,
+                    height: 80,
+                    child: mouseRegionWithOptionalOpaque(
+                      opaque: opaqueC,
+                      onEnter: (PointerEnterEvent e) { addLog('enterC'); },
+                      onExit: (PointerExitEvent e) { addLog('exitC'); },
+                    ),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      );
+    }
+
+    testWidgets('a transparent one should allow MouseRegions behind it to receive pointers', (WidgetTester tester) async {
+      final List<String> logs = <String>[];
+      await tester.pumpWidget(tripleRegions(
+        opaqueC: false,
+        addLog: (String log) => logs.add(log),
+      ));
+
+      final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+      await gesture.addPointer();
+      addTearDown(gesture.removePointer);
+      await tester.pumpAndSettle();
+
+      // Move to the overlapping area
+      await gesture.moveTo(const Offset(75, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['enterA', 'enterC', 'enterB']);
+      logs.clear();
+
+      // Move to the B only area
+      await gesture.moveTo(const Offset(25, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['exitC']);
+      logs.clear();
+
+      // Move back to the overlapping area
+      await gesture.moveTo(const Offset(75, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['enterC']);
+      logs.clear();
+
+      // Move to the C only area
+      await gesture.moveTo(const Offset(125, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['exitB']);
+      logs.clear();
+
+      // Move back to the overlapping area
+      await gesture.moveTo(const Offset(75, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['enterB']);
+      logs.clear();
+
+      // Move out
+      await gesture.moveTo(const Offset(160, 160));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['exitA', 'exitB', 'exitC']);
+    });
+
+    testWidgets('an opaque one should prevent MouseRegions behind it receiving pointers', (WidgetTester tester) async {
+      final List<String> logs = <String>[];
+      await tester.pumpWidget(tripleRegions(
+        opaqueC: true,
+        addLog: (String log) => logs.add(log),
+      ));
+
+      final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+      await gesture.addPointer();
+      addTearDown(gesture.removePointer);
+      await tester.pumpAndSettle();
+
+      // Move to the overlapping area
+      await gesture.moveTo(const Offset(75, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['enterA', 'enterC']);
+      logs.clear();
+
+      // Move to the B only area
+      await gesture.moveTo(const Offset(25, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['enterB', 'exitC']);
+      logs.clear();
+
+      // Move back to the overlapping area
+      await gesture.moveTo(const Offset(75, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['enterC', 'exitB']);
+      logs.clear();
+
+      // Move to the C only area
+      await gesture.moveTo(const Offset(125, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>[]);
+      logs.clear();
+
+      // Move back to the overlapping area
+      await gesture.moveTo(const Offset(75, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>[]);
+      logs.clear();
+
+      // Move out
+      await gesture.moveTo(const Offset(160, 160));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['exitA', 'exitC']);
+    });
+
+    testWidgets('opaque should default to true', (WidgetTester tester) async {
+      final List<String> logs = <String>[];
+      await tester.pumpWidget(tripleRegions(
+        opaqueC: null,
+        addLog: (String log) => logs.add(log),
+      ));
+
+      final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse);
+      await gesture.addPointer();
+      addTearDown(gesture.removePointer);
+      await tester.pumpAndSettle();
+
+      // Move to the overlapping area
+      await gesture.moveTo(const Offset(75, 75));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['enterA', 'enterC']);
+      logs.clear();
+
+      // Move out
+      await gesture.moveTo(const Offset(160, 160));
+      await tester.pumpAndSettle();
+      expect(logs, <String>['exitA', 'exitC']);
+    });
+  });
+
   testWidgets('RenderMouseRegion\'s debugFillProperties when default', (WidgetTester tester) async {
     final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
     RenderMouseRegion().debugFillProperties(builder);